1. Field of the Invention
The present invention generally relates to laser scanning systems for, and methods of, scanning, reading and/or analyzing bar code symbols and, more particularly, to a miniature laser scanning system which is completely field-portable due to its light-weight and small-size and small-volume characteristics. Still more particularly, this invention relates to a hand-held laser scanning head in which the laser source, power component, optics, scanning elements, sensors, and signal processing circuitry are all mounted therein. Yet more particularly, this invention relates to new high-speed scanning elements and their methods of scanning.
2. Description of the Prior Art
Many industries, particularly the grocery and food processing industry, have begun to designate their products with a unique bar code symbol consisting of a series of lines and spaces of varying widths. Various bar code readers and laser scanning systems have been developed to decode the symbol pattern to a multiple digit representation for check-out and inventory purposes.
For example, the contact-type wand or pen bar code readers were manually positioned on the symbol, and then manually dragged across the symbol, with the pen tip always remaining in contact with the symbol. Skilled personnel were generally required to effect the movement, because, among other factors, the angle and pressure of the pen on the symbol was somewhat critical, and the speed of the pen during its manual movement, as well as the uniformity of the pen speed, were also critical.
These contact-type pens were disadvantageous not only because of the requirement for skilled personnel, but also because the pen tip tended to scar the symbol itself. Repetitive manual sweeps were often necessary, because successful decoding may not have occurred on the first attempt. Also, in some applications, a product may need to be scanned several times a day, or repetitively over the years. To protect the symbols, mylar protective coatings were used; however, the mylar coating is not only expensive, but also diffuses the light, thereby resulting in reading problems.
The lack of uniformity of the pen speed also means that the pen readers could not be reliably used as scanner, and particularly not for accurately measuring line widths in symbol analyzers, which measurement requires a uniform scanning speed.
Contact-type pen readers cannot be used with wax-coated products, such as milk cartons, because the was diffuses the light and also adheres to the pen tip, thereby necessitating constant cleaning of the tip.
Nor can contact-type readers be used on soft products, such as soft-packaged potato chips, cheese, or blood bags. The user would have to follow the wrinkles with the pen over these soft packages, and might even rip the package itself.
Nor can contact-type readers be used where the bar code symbol is located on the outer surface of relective aluminum cans; also, contact-type readers cannot be used where the symbol is not located at the outer surface of the packaging. For example, cassette tapes are coded, but the plastic container for the cassette spaces the symbol at a small, but non-negligible, distance from the outer plastic surface of the container across which the pen is dragged. This small distance can cause light diffusion and non-reading.
Some wand or pen readers are of the non-contact type, i.e., the pen tip need not be in physical contact with the symbol. Nevertheless, the depth of focus is not large, and the pen must be positioned in the immediate vicinity of the symbol. For all practical purposes, the non-contact pens are usually manually dragged across the symbol, thereby resulting in the scarring and cleaning problems discussed above.
Moreover, non-contact pens still require criticality in the manipulation of the angle of the pen on the symbol, the pen speed, the pen pressure and the uniformity of pen speed. Most importantly, just like the contact-type pens, the user, at best, gets one scan per manual movement. If the symbol was not successfully read on the first attempt, then the user must repeat the manual scan again and again until a successful decode has been performed. This is time- and labor-consuming.
True laser scanners, not manual readers, are built-into supermarket counters. These point-of-sale of "deck" scanners may be of the moving beam or fixed beam type. However, these are large, massive, stationary installations. Some objects are to heavy, or too big, or too inconvenient to be brought to the stationary scanning installation. Some objects may be stationary themselves.
More modern scanners have recently been designed to have hand-held, portable laser scanning heads. However, the known portable heads weigh over three pounds and are too heave for those assembly-line applications where a user is reading codes all day long. The known portable heads are also somewhat difficult to manipulate easily due to their size, as well as due to the fact that a rather thick and somewhat unwieldly cable interconnects the portable head to a desk-top console which houses the decode circuitry. The cable contains relatively thick, shielded wires and a relatively thick power wire which do not permit a relatively easy freedom of movement as the portable head is manipulated.